Not an answer to your question, but maybe interesting: A colleague of my father made some etched copper plate images from photos. I don't have his full process

Not an answer to your question, but maybe interesting: A colleague of my father made some etched copper plate images from photos. I don't have his full process, but he photocopied the original photos a few times to get an image made from black and white regions. This he photocopied onto a transparency, which he then used to etch a copper plate using a circuit etching kind of workflow. The final plate had smooth or matte copper areas corresponding to light and dark. Quite striking and I guess it should last a long time.